Estrus is detectable by a females behaviour in the presence of adult males.Normally cows allow bulls to approach and check their reproductive status.But a female approaching estrus is wary of bulls:she carries her head higher than normal,her eyes are wide open and watchful instead of downcast,and she moves quickly out of the way of an approaching adult male.If persistently approached and followed,she leaves the heard and walks happily away,with head high and/or turned to one side as she looks back at her escort(s)and tail raised.She maintains a lead of 10-75m and eventually circles back to rejoin her family.
If the bull is aroused to the point of having an erection and attempts to overtake her,the "estrous walk" turns into a chase,during which the female may go a kilometer or more from the heard over a period of several hours.The cow stops fleeing when and if a bull gets within touching distance,whereupon he attempts to mount her.First he lays his trunk along her neck and head,then rests his own tusks or chin on her rump and levers himself onto his bent hindlegs,resting his forefeet on her pelvis.
A cooperative cow holds still or backs into him.As his penis grows fully erect(weighing then over 27kg),it curves forward and upward,probing for the entrance to the vagina.After achieving intromission,the bull straightens his hind legs and assumes a normal mounting posture. Mounting and copulation are completed within 45 seconds,without thrusting or apparent ejaculatory pause.Sometimes one or both rumble,groan or scream.After the bull dismounts the cow may run off,but most stand still.
The distraught behaviour of elephant cows during the 2-6 day estrus creates a disturbance and often excites other elephants.Chasing and particularly copulation may provoke ear flapping,head-shaking,and loud vocalizing.While a pair is copulating,other herd members may back towards them,urinating and defecating.One result of the commotion is to bring other bulls to the scene,which then proceed to compete for mating rights-supplanting,chasing,thereat,shoving,tusk-poking and sometimes fighting one another.On 154 occasions when estrous females were observed in Amboseli N.P. an average of ten adult bulls(25yrs and older)were present.Not only did older and bigger bulls dominate young animals but cows also clearly preferred to mate with them.Out of 134 chases,cows eluded all but 30.6% of their pursuers,medium and large bulls accounted for 83% of the chases that ended in copulation.Furthermore,the 19 largest bulls in the population of a 160 adult males performed 65% of the observed copulations.And among them,the 1 or 2 bulls that happened to be in musth at any given time were continually in quest of mating opportunities,dominated all other elephants,and were preferred above by all others by estrous cows.Apart from heightened aggression associated with elevated testosterone levels,musth is revealed by the copious and viscous secretions of the temporal glands,and a swollen and partially extended penis which drips a green,strong smelling secretion.When a large bull in musth stays with a herd,it usually indicates he is in courtship with an estrous female.Not only does the bull follow her,but the cow stays close to him(and sometimes solicits mating),especially when other bulls attempt to court her.Because other males give a bull in musth a wide berth,females consorting with them thereby escape much of the harassment that can make estrus stressful and exhausting.